It is known that a flat sheet or board can be reinforced, e.g. by corrugating the sheet, or by moulding or pressing a pattern into the sheet or board. See GB 2,336,566A of S. P. Carrington, which shows that complex corrugations encompassing two or more conceptual axes can increase bending stiffness of the sheet.
At present bending wave panel-form acoustic radiators are normally made from composites comprising a core sandwiched between skin layers, although alternatively such radiators may be monolithic sheet-like structures, e.g. of plastics, metal or card.
In addition, it is known from WO00/15000 of New Transducers Limited to stiffen a panel-form acoustic radiator such that its bending stiffness varies over its area.
It is also known from WO00/65869 of New Transducers Limited to dish the portion of a bending wave panel of a loudspeaker located within the contact ring of the voice coil of a moving coil vibration transducer mounted on the panel to provide local stiffening of the panel to control aperture resonance.
It is an object of the invention to provide a simple and relatively inexpensive bending wave panel-form acoustic radiator.